"Suppose a man threw into the sea a yoke with one hole in it, and the east wind carried it to the west, and the west wind carried it to the east, and… - The Buddha

"Suppose a man threw into the sea a yoke with one hole in it, and the east wind carried it to the west, and the west wind carried it to the east, and the north wind carried it to the south, and the south wind carried it to the north. Suppose there were a blind turtle that came up once at the end of each century. What do you think, bhikkhus? Would that blind turtle put his neck into that yoke with one hole in it?"
"He might, venerable sir, sometime or other at the end of a long period."
"Bhikkhus, the blind turtle would sooner put his neck into that yoke with a single hole in it than a fool, once gone to perdition, would take to regain the human state, I say. Why is that? Because there is no practising of the Dhamma there, no practising of what is righteous, no doing of what is wholesome, no performance of merit. There mutual devouring prevails, and the slaughter of the weak."